per the Working Time Directive, as stated by Bednobs - you may not take your break at the start/end of the working day; therefore you cannot insist on taking an early day after working through.
My last employer would let you work through your break and finish your work that much earlier, but you had to be there at 5 to clock out!
That said, if it suits everybody, I can't see anyone breaking down your door with a stopwatch. But if just one person objects and reports it, you will be stopped.